The 2D flow presented here is driven by an external force, which generates a spinning motion according to a repeated, regular pattern. This situation is illustrated by the left figure, which displays the fluid vorticity in an early stage, where the fluid velocity is parallel to the force. Red areas are clock-wise rotating, and blue areas counter-clockwise. Boundary conditions are periodic, the lattice resolution is 2000×2000, and the Reynolds number is Re=2000. After an initial laminar stage, the fluid enters a turbulent regime, in which the flow does not reflect any more the structure of the force field. This is visible on the right picture and on the animations.